2021A&A...650A..33P


Query : 2021A&A...650A..33P

2021A&A...650A..33P - Astronomy and Astrophysics, volume 650A, 33-33 (2021/6-1)

A systematic search for changing-look quasars in SDSS-II using difference spectra.

POTTS B. and VILLFORTH C.

Abstract (from CDS):


Context. 'Changing-look quasars' (CLQs) are active galactic nuclei (AGN) showing extreme variability that results in a transition from type 1 to type 2 AGN. The short timescales of these transitions present a challenge to the unified model of AGN and the physical processes causing these transitions remain poorly understood. CLQs also provide interesting samples for the study of AGN host galaxies since the central emission disappears almost entirely.
Aims. Previous searches for CLQs have utilised photometric variability or SDSS classification changes to systematically identify CLQs; this approach may miss lower luminosity CLQs. In this paper, we aim to use spectroscopic data to asses if analysis difference spectra can be used to detect further CLQs that have been missed by photometric searches.
Methods. We searched SDSS-II DR 7 repeat spectra for sources that exhibit either a disappearance or appearance of both broad line emission and accretion disc continuum emission by directly analysing the difference spectrum between two epochs of observation.
Results. From a sample of 24782 objects with difference spectra, our search yielded six CLQs within the redshift range 0.1≤z≤0.3, including four newly identified sources. Spectral analysis indicates that changes in the accretion rate can explain the changing-look behaviour. While a change in dust extinction fits the changes in the spectral shape, the timescales of the changes observed are too short for obscuration from torus clouds.
Conclusions. Using difference spectra was shown to be an effective and sensitive way to detect CLQs. We recover CLQs an order of magnitude lower in luminosities than those found by photometric searches and achieve higher completeness than spectroscopic searches relying on pipeline classification.

Abstract Copyright: © ESO 2021

Journal keyword(s): galaxies: active - accretion - accretion disks

Simbad objects: 9

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Number of rows : 9
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 SDSS J000236.25-002724.7 Sy1 00 02 36.2488238640 -00 27 24.672082968   19.99 19.36     ~ 13 0
2 [VV2003c] J012648.1-083948 Sy1 01 26 48.0892245120 -08 39 48.056230224   19.27 18.81     ~ 23 0
3 2MASS J01595763+0033105 Sy1 01 59 57.6419121888 +00 33 10.497849444   20.31 19.66     ~ 94 0
4 SDSS J082323.89+422048.2 SyG 08 23 23.8964598456 +42 20 48.209247384   19.05 18.47     ~ 11 0
5 LEDA 2188986 Sy1 08 29 42.6782568912 +41 54 36.832341204   19.07 18.45     ~ 40 0
6 NGC 4151 Sy1 12 10 32.5759813872 +39 24 21.063527532   12.18 11.48     ~ 3669 2
7 SDSS J135855.82+493414.1 Sy1 13 58 55.8280155192 +49 34 14.060697492           ~ 11 0
8 1RXS J172321.6+550417 Sy1 17 23 22.3111874328 +55 04 13.827859680   19.81 19.25     ~ 10 0
9 [VV2003c] J233603.0+001728 Sy1 23 36 02.9868147432 +00 17 28.773473892   20.18 19.66     ~ 23 0

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